Cooling System, Method for Operating the Same, and Plasma Processing System Using Cooling System

ABSTRACT

In a cooling system, a compressor ( 1 ), a heat source ( 2 ), a heat exchanger ( 3 ), and a buffer tank ( 4 ) are connected in that order by piping ( 5 ) to constitute a closed circuit. In the closed circuit, nitrogen serving as a refrigerant is circulated without contacting open air. Any gas except for the air may be used as the refrigerant as long as the gas absorbs heat from the heat source ( 2 ) and dissipates the heat to the outside in the heat exchanger ( 3 ) when the gas is circulated in the closed circuit without being liquefied.

TECHNICAL FIELD

The present invention relates to a cooling system which cools a heat source with a refrigerant, a method for operating the cooling system, and a plasma processing system in which the cooling system is used.

BACKGROUND ART

Conventionally a heat pump is used. The heat pump is a system for cooling and heating. Vaporization heat is utilized in the heat pump. The vaporization heat is heat which the refrigerant absorbs from the surroundings when the refrigerant is transformed from liquid into gas. Condensation heat is also utilized in the heat pump. The condensation heat is also heat which the refrigerant dissipates to the surroundings when the refrigerant is transformed from the gas into the liquid. In the heat pump, a compressor, a heat exchanger and the like are used to utilize the vaporization heat and condensation heat.

More specifically, the heat pump is used in an internal combustion engine or a refrigerator. A cooling system including a closed circuit is usually incorporated in the internal combustion engine or refrigerator. In the cooling system, a liquid refrigerant such as a chlorofluorocarbon gas is vaporized by adiabatic expansion. The compressor compresses the vaporized refrigerant in an adiabatic state. This enables the vaporized refrigerant to be condensed to return to the liquid refrigerant. The heat exchange cycle is repeated. A large heat quantity can efficiently be exchanged in the heat exchange cycle.

On the other hand, a furnace, a tank, a chimney or the like have an extremely large surface area in a large-scale plant. The vaporization heat of the refrigerant flowing in refrigerant piping provided in a meandering manner along the surface of the large-scale plant is used in cooling the large-scale plant having the large surface area. In this case, while the rapid cooling is performed at a position near an entrance of the refrigerant piping by the vaporization heat, the cooling is not performed at a position near an exit of the refrigerant piping by the vaporization heat because the liquid refrigerant is already vaporized. When the large-scale plant is cooled using a heat exchange cycle accompanied by the phase change between the liquid and the gas, extreme unevenness is generated in a surface temperature distribution of the large-scale plant. Therefore, nitrogen or an inert gas such as argon which has small specific heat is used as the refrigerant of the heat pump for cooling the particular large-scale plant facilities.

Patent Document 1: Japanese Patent Laying-Open No. 1-193561 Patent Document 2: Japanese Patent Laying-Open No. 2003-329355 DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

The following problems exist in the conventional heat pump in which the gas is used as the refrigerant to utilize the vaporization heat and condensation heat.

First it is considered that the gas is used as the refrigerant for cooling the heat source in the closed circuit of the heat pump. When the cooling is performed by utilizing the vaporization heat and condensation heat, sometimes all the gases are transformed into the liquid between the entrance and exit of a cooling tube. In such a case, a heat absorbing ability of the refrigerant largely depends on a position of the cooling tube. Therefore, because the large unevenness is generated in the temperature distribution of the cooling tube, the heat source cannot evenly be cooled.

Then, it is considered that the gas is not circulated in the closed circuit, but the heat source is cooled by a method in which the gas is sequentially discharged after passing through an open circuit. Generally the gas has the extremely small specific heat compared with the liquid such as water. Therefore, in this case, because discharge of a large amount of gas is required depending on a form of the open circuit, consumption of the gas becomes extremely large. As a result, the running cost is largely increased in the heat pump. Although the gas can be reused for other applications, a large drawback is generated from the viewpoint of cost because large-scale facility is required for the reuse of the gas.

Then, it is considered that normal cooling water is used as the refrigerant to cool the heat source. In this case, due to the large specific heat of the water, the unevenness of the surface temperature distribution is increased in the large heat source. Accordingly, the cooling system in which the water is used as the refrigerant is not suitable to the cooling system in which the heat source is evenly cooled. In a case where the heat source is placed in a vacuum atmosphere, or in a case where a substance reacting easily with the water exists in an ambient atmosphere, when the water leaks from the cooling tube, vapor explosion is possibly caused by pressuring a vacuum chamber to an atmospheric pressure, or surrounding parts of the cooling system are possibly broken by the reaction of the leaked water with the ambient atmosphere.

Then, it is considered that a temperature is controlled using pressurized water like a mold temperature controller. In this case, it is impossible in principle to cool the heat source having a temperature not lower than 160° C. Similarly the vapor explosion and the breakage of the surrounding parts of the cooling system are possibly generated.

In view of the foregoing, an object of the present invention is to provide a cooling system which can evenly cool the large heat source, a method for operating the cooling system, and a plasma processing system in which the cooling system is used.

Means for Solving the Problems

A cooling system according to the present invention includes a compressor to compress a gas refrigerant except air to a degree in which the gas refrigerant is not liquefied and to deliver the gas refrigerant; a heat source to be cooled by the gas refrigerant when the gas refrigerant delivered from the compressor passes therethrough; a heat exchanger in which the gas refrigerant dissipates heat to an outside after absorbing the heat from the heat source; a buffer tank in which the gas refrigerant is temporarily accumulated after dissipating the heat to the outside in the heat exchanger; and piping to couple the compressor, the heat source, the heat exchanger, and the buffer tank in that order to constitute a closed circuit, the gas refrigerant being circulated through the piping.

According to the above-described configuration, because the heat source is cooled using the gas refrigerant having small specific heat, when the heat source having a large surface area is cooled, a level at which the unevenness of the temperature distribution is generated in the surface of the heat source can be reduced compared with a case where a liquid having the large specific heat is used or a case where the heat source is cooled by the phase change of the refrigerant. When gas is used as the refrigerant, a trouble caused by the reaction of the gas with another substance is possibly generated. However, according to the configuration, a risk of generating the trouble is eliminated because the gas refrigerant is circulated in the closed circuit.

Further, preferably the cooling system further includes another buffer tank the compressor and the heat source to temporarily accumulate the gas refrigerant therein.

A volume of the buffer tank is preferably not lower than an amount of the gas refrigerant discharged by the compressor within a time necessary to circulate the gas refrigerant once in the closed circuit. Accordingly, a risk of depletion of the gas refrigerant discharged by the compressor is reduced.

Moreover, preferably the cooling system further includes replenishing piping connected to the buffer tank to replenish the gas refrigerant from the outside; and discharging piping connected to the buffer tank to discharge the gas refrigerant to the outside.

According to the above-described configuration, the gas refrigerant can be replenished to the buffer tank from the outside through the replenishing piping when the gas refrigerant amount is excessively small in the buffer tank, and the gas refrigerant can be discharged to the outside through the discharging piping when the gas refrigerant amount is excessively large in the buffer tank.

Further, preferably the compressor has an ability to discharge an amount of the gas refrigerant larger than a circulating amount of the gas refrigerant necessary to cool the heat source to a target temperature. Accordingly, the state in which the supply of gas refrigerant to the heat source runs short is not generated.

The gas refrigerant preferably contains nitrogen, oxygen, carbon dioxide, or inert gas. Because these gas refrigerants have a low risk of reacting with other substances, the gas refrigerants have a low risk of negatively affecting an ambient environment in a case where the gas refrigerants leak to the outside of the closed circuit.

The piping acts as a cooling tube in the heat source. When a surface area of the cooling tube is in a range of 20 cm² to 750 cm² per 1 m³ of heat source, the heat exchange can sufficiently be performed.

When pressure loss of the gas refrigerant in the heat exchanger is not more than one-tenth of pressure loss of the gas refrigerant in the entire closed circuit, the heat exchanger does not obstruct the flow of the gas refrigerant necessary to cool the heat source.

When the cooling system according to the present invention further includes a refrigerant supply path aside from the closed circuit, the refrigerant supply path capable of supplying to the compressor the gas refrigerant of an amount discharged by the compressor until the gas refrigerant is circulated once in the closed circuit since the compressor is started up, running is stabilized immediately after the compressor is started up.

In the cooling system according to the present invention, preferably the cooling system further includes an exhaust valve to automatically exhaust the gas refrigerant in the buffer tank when a pressure of the gas refrigerant in the buffer tank is substantially equal to an upper limit of a suction pressure of the compressor; and a suction valve to automatically suck the gas refrigerant into the buffer tank when the pressure of the gas refrigerant in the buffer tank is substantially equal to a lower limit of the suction pressure of the compressor. Accordingly, safety of the buffer tank and the proper operating state of the compressor can automatically be ensured.

A plasma processing system according to the present invention includes a compressor to compress a gas refrigerant except air to a degree in which the gas refrigerant is not liquefied and to deliver the gas refrigerant; a plasma processing apparatus to generate heat when a predetermined process is performed using a plasma processing gas, the plasma processing apparatus being cooled by the gas refrigerant when the gas refrigerant delivered from the compressor passes therethrough; a heat exchanger in which the gas refrigerant dissipates heat to an outside after absorbing the heat from the heat source; a buffer tank in which the gas refrigerant is temporarily accumulated after dissipating the heat to the outside in the heat exchanger; and piping to couple the compressor, the heat source, the heat exchanger, and the buffer tank in that order to constitute a closed circuit, the gas refrigerant being circulated through the piping, wherein the gas refrigerant includes one or more gases which does not react with the plasma processing gas.

In accordance with the present invention, a method for operating a cooling system relates to a method for operating the above-described cooling system, and the method includes the steps of sucking the gas refrigerant into the buffer tank by a decrease in pressure of the gas refrigerant in the buffer tank when the compressor is started up; and maintaining a pressure of the gas in the buffer tank at a value of a degree in which the compressor is not broken, after a time longer than a time necessary to circulate the gas refrigerant once in the closed circuit elapses. Accordingly, because the state in which the gas refrigerant is not supplied to the compressor is not generated, the breakage of the compressor is prevented.

EFFECTS OF THE INVENTION

According to the present invention, because the gas having the small specific heat is used as the refrigerant, the unevenness of the temperature is hardly generated in the surface of the heat source. The increase in running cost can be suppressed because the gas refrigerant is circulated in the closed circuit. Because the type of the gas can arbitrarily selected, when the gas having the low risk is used according to an atmosphere around the heat source, the heat source can safely be cooled. Furthermore, in the cooling system of the present invention, the cooling ability can be adjusted relatively easily because the phase change between the gas and the liquid is not utilized.

The above and further objects, features, aspects, and advantages of the invention will appear from the following detailed description with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing a configuration of a cooling system according to an embodiment.

FIG. 2 is a view showing a compressor used in the cooling system of the embodiment.

FIG. 3 is a view showing a configuration of a cooling system of another example of the embodiment.

FIG. 4 is a view showing a heat source used in the cooling system of the embodiment.

FIG. 5 is a view showing a heat exchanger used in the cooling system of the embodiment.

FIG. 6 is a view showing a buffer tank used in the cooling system of the embodiment.

DESCRIPTION OF THE REFERENCE SIGNS

1 compressor, 2 heat source (large heater), 3 heat exchanger, 4 buffer tank

BEST MODES FOR CARRYING OUT THE INVENTION

A cooling system according to an embodiment of the present invention will be described with reference to the drawings.

The cooling system of the embodiment is used to cool a heat source such as a large heater in which the cooling is required while a surface temperature distribution is evenly maintained. In the embodiment, it is assumed that the heat source to be cooled is placed in an atmosphere reacting easily with oxygen. Therefore, it is perceived that nitrogen or argon is used as a refrigerant of the cooling system. However, the refrigerant should appropriately be selected according to an atmosphere around the heat source, and any gas may be used without limiting to the nitrogen or argon. In the cooling system of the present embodiment, each instrument used is illustrated only by way of example, and each instrument used in the cooling system of the present invention is not limited to the instrument described below.

Referring to FIG. 1, an entire configuration of a cooling system 100 of the embodiment will be described.

Cooling system 100 of the present embodiment includes a compressor 1 as shown in FIG. 1. Compressor 1 sucks the refrigerant accumulated in a buffer tank 4, and compressor 1 compresses and delivers the refrigerant. The nitrogen is used as the refrigerant delivered by compressor 1 in consideration of a price and a heat conductivity. The nitrogen draws the heat from a heat source 2 to cool heat source 2 when passing through heat source 2. The nitrogen drawing the heat from heat source 2 reaches a heat exchanger 3. In heat exchanger 3, the nitrogen dissipates the heat to the outside, which lowers a temperature of the nitrogen. Then, the nitrogen reaches buffer tank 4, and the nitrogen is temporarily accumulated.

In the present embodiment, compressor 1, heat source 2, heat exchanger 3, and buffer tank 4 are connected in that order by piping 5 through which the nitrogen flows, thereby constituting a closed circuit in which the nitrogen is circulated without contacting open air. Any gas except for the air may be used as the refrigerant circulated in the closed circuit, as long as the gas absorbs the heat from the heat source and dissipates the heat to the outside when the gas is circulated in the closed circuit without being liquefied.

According to the above-described cooling system of the present embodiment, because heat source 2 having a large surface area is cooled using the nitrogen having small specific heat, a level at which the unevenness of the temperature distribution is generated in the surface of heat source 2 can be reduced as compared with a case where a liquid having the large specific heat is used or a case where the heat source is cooled by the phase change of the refrigerant. When the nitrogen is used in the atmosphere reacting with the nitrogen, the trouble caused by the reaction of the nitrogen with another substance is possibly generated. However, in the present embodiment, a risk of generating the trouble is eliminated because the nitrogen is circulated in the closed circuit.

For example, in compressor 1, rotation of a rotating body 1 c rotated by a motor (not shown) is transferred to a piston 1 a by a crank as shown in FIG. 2. Therefore, piston 1 a is reciprocated in a cylinder 1 e. As shown by arrows in FIG. 1, the nitrogen flowing through piping 5 is sucked from an inlet port 1 f into cylinder 1 e. In cylinder 1 e, the nitrogen is compressed by piston 1 a, which opens a flat spring valve 1 d by the nitrogen whose pressure is enhanced. Accordingly, as shown by arrows in FIG. 2, the nitrogen in cylinder 1 e is discharged from an exhaust port 19 into piping 5. The gaseous nitrogen is discharged by compressor 1. That is, compressor 1 compresses the nitrogen to an extent that the gaseous nitrogen is not liquefied and discharges the gaseous nitrogen.

Compressor 1 has an ability to discharge a gas amount larger than a necessary gas circulating amount in order to cool heat source 2 to a target temperature. Accordingly, supply of the nitrogen to heat source 2 does not run short.

The cooling system of the present embodiment includes another nitrogen supply path aside from the closed circuit. Through another nitrogen supply path, the nitrogen amount discharged by compressor 1 is supplied to compressor 1 while the nitrogen is circulated once in the closed circuit after compressor 1 is started up. Specifically, as shown in FIG. 1, another nitrogen supply path is nitrogen replenishing piping 8 a connected to buffer tank 4. Accordingly, immediately after compressor 1 is started up, a nitrogen replenishment control valve 80 a is opened to supply the nitrogen into buffer tank 4 from a nitrogen tank 200, and the nitrogen is sequentially delivered to compressor 1. Therefore, running is stabilized immediately after compressor 1 is started up. In the closed circuit shown in FIG. 1 six seconds are required to circulate the nitrogen once at a rate of 1 m³/min.

In the present embodiment, it is assumed that the heat quantity of about 50 Kcal/cm²/h is evenly removed from the large heater serving as heat source 2. Therefore, assuming that a temperature difference of 150° C. exists between the large heater and the nitrogen serving as the refrigerant, it is necessary that the nitrogen be always circulated at the rate of 1 m³/min in the closed circuit. Accordingly, compressor which can circulate the nitrogen with the discharge amount not lower than 1 m³/min is selected as compressor 1. However, it is necessary that the discharge amount of compressor 1 be determined in consideration of pressure loss of the entire piping 5. Preferably the nitrogen discharge amount of compressor 1 is not lower than 1.2 times of the necessary nitrogen circulating amount, and more preferably 1.5 times of the necessary nitrogen circulating amount. This enables the circulating flow rate of the nitrogen to be sufficiently ensured in consideration of the pressure loss caused by curved portions of piping 5 and valves provided in piping 5.

As shown in FIG. 3, another buffer tank 6 may be provided between compressor 1 and heat source 2 in order to release a fluctuation in operation rate of compressor 1 according to a load change. Buffer tank 6 temporarily accumulates the gas, and buffer tank 6 is resistant to a high pressure. This enables the flow rate of the gas to be stably supplied to heat source 2. However, buffer tank 6 is provided as needed, and buffer tank 6 is not necessarily provided in the present invention.

Because heat source 2 has the large surface area, piping 5 through which the nitrogen is circulated is provided in a meandering way as shown in FIG. 4. The nitrogen is delivered from compressor 1 through an entrance 2 a into the meandering piping 5 in heat source 2. The nitrogen passing through heat source 2 is delivered to piping 5 through an exit 2 b. According to cooling system 100 of the present embodiment, because the nitrogen having the small specific heat is used as the refrigerant, a heat exchange ability of the nitrogen near entrance 2 a of heat source 2 is substantially equal to a heat exchange ability of the nitrogen near exit 2 b of heat source 2. Consequently, the unevenness of the temperature distribution is not generated in the surface of the heat source 2.

As shown in FIG. 5, piping 5 is provided in the meandering way in heat exchanger 3. The nitrogen passing through heat source 2 is delivered through an entrance 3 a to the meandering piping 5 in heat exchanger 3, and the heat is dissipated to the outside while the nitrogen flows through the meandering piping 5. In heat exchanger 3, the heat of the nitrogen is transferred to cooling water flowing from entrance piping 7 a toward exit piping 7 b. The nitrogen passing through heat exchanger 3 is discharged to piping 5 through an exit 3 b.

As shown in FIG. 1, the cooling water is accumulated in a cooling water tank 300, and the cooling water is circulated between cooling water tank 300 and heat exchanger 3 by a cooling water pump 310. Accordingly, the temperature is lowered in the nitrogen passing through heat exchanger 3, and the temperature becomes a degree in which the heat can be drawn from heat source 2 when passing through heat source 2. Cooling water pump 310 is controlled by a controller 30. In cooling water tank 300, a cooling fan is provided to perform heat exchange between the air and the cooling water.

The pressure loss of the nitrogen in heat exchanger 3 is not more than one-tenth of the pressure loss of the nitrogen in the entire closed circuit. Accordingly, heat exchanger 3 does not obstruct the flow of the nitrogen necessary to cool heat source 2.

The surface area of piping 5 serving as a cooling tube in heat source 2 is in a range of 20 cm² to 750 cm² per 1 m³ of heat source. Accordingly, heat source 2 has the sufficient heat exchange ability.

Generally it is necessary that heat exchanger 3 perform the heat exchange of an amount except a heat dissipation amount of the nitrogen in piping 5. However, in the present embodiment, even if the heat dissipation amount of piping 5 is negligible, it is necessary that heat exchanger 3 be able to perform the heat exchange not lower than about 50 Kcal/cm²/h. Because a large amount of nitrogen gas is required to flow in piping 5 in heat exchanger 3, it is necessary to reduce the pressure loss of piping 5. Additionally, it is necessary to smoothly perform the heat exchange. Therefore, desirably piping 5 is made of a material, such as copper and aluminum, which has the large heat conductivity. This enables a size of heat exchanger 3 to be reduced.

As shown in FIG. 6, piping 5 is also connected to buffer tank 4, the nitrogen in which the heat exchange is already performed in heat exchanger 3 is introduced through an entrance 4 a, and the nitrogen is accumulated in buffer tank 4. Then, the nitrogen is sucked from buffer tank 4 into compressor 1 in each time a space in cylinder 1 e becomes negative pressure by reciprocating motion of piston 1 a of compressor 1. The nitrogen in buffer tank 4 is delivered to piping 5 through an exit 4 b.

A volume of buffer tank 4 is not lower than the amount of nitrogen which is discharged by compressor 1 within the time necessary for the one-time circulation of the nitrogen in the closed circuit. More specifically, the volume of buffer tank 4 is not lower than 100 L. Desirably the volume of buffer tank 4 has a high factor of safety because the volume of buffer tank 4 has a large influence on the stability of the closed circuit. Specifically, preferably the factor of safety of the buffer tank 4 is not lower than two. The factor of safety of two means that the volume of 200 L is ensured for the necessary volume of 100 L. According to the above-described configuration, the nitrogen discharged by compressor 1 does not run short in buffer tank 4, which prevents the generation of continuous driving of compressor 1 in spite of no nitrogen supplied to compressor 1. Therefore, a risk of breakage of compressor 1 is reduced.

As shown in FIG. 6, buffer tank 4 is connected to nitrogen replenishing piping 8 a for replenishing the nitrogen from the outside and to nitrogen discharging piping 8 b for discharging the gas to the outside. As shown in FIG. 1, nitrogen replenishing piping 8 a and nitrogen discharging piping 8 b are connected to a nitrogen tank 200. A nitrogen replenishing pump 210 is provided in nitrogen replenishing piping 8 a. A nitrogen discharging pump 220 is provided in nitrogen discharging piping 8 b.

Nitrogen replenishment control valve 80 a and a nitrogen discharge control valve 80 b are provided in nitrogen replenishing piping 8 a and nitrogen discharging piping 8 b respectively. Controller 30 controls nitrogen replenishment control valve 80 a, nitrogen discharge control valve 80 b, nitrogen replenishing pump 210, and nitrogen discharging pump 220. Controller 30 receives a signal which can specify a measured value of a pressure sensor 20 provided in buffer tank 4, and controller 30 controls nitrogen replenishment control valve 80 a, nitrogen discharge control valve 80 b, nitrogen replenishing pump 210, and nitrogen discharging pump 220 based on the signal. Controller 30 also controls compressor 1.

During running of the cooling system of the present embodiment, because the nitrogen is supplied into buffer tank 4 by the decrease in gas pressure in buffer tank 4 due to the start-up of compressor 1 immediately after compressor 1 is started up, controller 30 drives nitrogen replenishing pump 210 while opening nitrogen replenishment control valve 80 a. After the time longer than the time necessary to circulate the nitrogen once in the closed circuit elapses, controller 30 controls opening and closing of nitrogen replenishment control valve 80 a and nitrogen discharge control valve 80 b and driving states of nitrogen replenishing pump 210 and nitrogen discharging pump 220 such that the gas pressure in buffer tank 4 is set to a value of a degree in which compressor 1 is not broken, for example, a positive pressure not more than 0.5 atmosphere.

That is, in a case where the nitrogen amount in buffer tank 4 is excessively small, controller 30 opens nitrogen replenishment control valve 80 a and drives nitrogen replenishing pump 210 to replenish the nitrogen from nitrogen tank 200 to buffer tank 4 through nitrogen replenishing piping 8 a. In a case where the nitrogen amount in buffer tank 4 is excessively large, controller 30 opens nitrogen discharge control valve 80 b and drives nitrogen discharging pump 220 to discharge the nitrogen from buffer tank 4 to nitrogen tank 200 through nitrogen discharging piping 8 b. Accordingly, because the state in which the nitrogen is not supplied to compressor 1 is not generated, the breakage of compressor 1 is prevented.

When controller 30 receives the signal from pressure sensor 20 to detect that the nitrogen pressure in buffer tank 4 is substantially equal to an upper limit of the suction pressure of compressor 1, controller 30 can close nitrogen replenishment control valve 80 a, close nitrogen discharge control valve 80 b, and automatically drive nitrogen discharging pump 220 to discharge the nitrogen in buffer tank 4. When controller 30 receives the signal from pressure sensor 20 to detect that the nitrogen pressure in buffer tank 4 is substantially equal to a lower limit of the suction pressure of compressor 1, controller 30 can close nitrogen discharge control valve 80 b, close nitrogen replenishment control valve 80 a, and automatically drive nitrogen replenishing pump 210 to suck the nitrogen into buffer tank 4. The upper limit and lower limit are values determined in each type of compressor 1, and compressor 1 and buffer tank 4 are not broken as long as the nitrogen having the amount within a range regulated by the values is supplied into buffer tank 4. Accordingly, according to the above-described configuration, the safety of buffer tank 4 and the proper operating state of compressor 1 can automatically be ensured.

Although the nitrogen is used as the refrigerant in the present embodiment, oxygen, carbon dioxide, or inert gas (for example, argon) may be used instead of the nitrogen. Because these gases have a low risk of reacting with other substances, the gases have a low risk of negatively affecting an ambient environment in a case where the gases leak to the outside of the closed circuit.

In particular, when the heat source placed in a high-temperature vacuum atmosphere is cooled using a liquid refrigerant, there is a risk of boiling the liquid to lead to the explosion such as the vapor explosion. Therefore, in such a case, the liquid refrigerant cannot be used in the cooling system. For example, like a plasma CVD (Chemical Vapor Deposition) apparatus, there is an apparatus forming the vacuum atmosphere slightly containing the highly reactive gas or the strongly toxic gas. The plasma processing apparatus generates the heat in a process of performing desired treatment using a predetermined gas. In a case of the use the cooling system in which the plasma processing apparatus is incorporated as heat source 2, desirably the gas refrigerant which does not react with the gas used in the plasma processing apparatus is used while cooling efficiency is considered. Therefore, the trouble caused by the reaction of the gases with each other (for example, chemical reaction) is not generated, even if the gas refrigerant leaks from piping 5 of the cooling system while the gas used for the plasma processing in the plasma processing apparatus leaks from the plasma processing apparatus. Accordingly, the safety is improved in the plasma processing system in which the cooling system is used. The gas refrigerant may be formed by either one kind of gas or plural kinds of gases.

According to cooling system 100 of the above-described embodiment, in a case where large heat source 2 is cooled, the high-temperature heat source 2 can be cooled without adopting the large-scale structure, the safety can be ensured, and the heat source can evenly be cooled without breaking the surrounding parts.

The method for operating the cooling system according to the embodiment will be described below. After compressor 1 is started up, controller 30 opens compressor 1 provided between buffer tank 4 and compressor 1 shown in FIG. 1. At this point, the nitrogen is supplied from nitrogen replenishing piping 8 a to buffer tank 4 to prevent the operation of compressor 1 in the negative-pressure state. In particular, because compressor 1 is easily operated in the negative-pressure state in a period during which the nitrogen is circulated to keep cooling system 100 in the steady state (within six seconds), it is necessary that the nitrogen be supplied to buffer tank 4.

Then, when the nitrogen is circulated through piping 5 of the closed circuit, the pressure is stabilized in buffer tank 4, and compressor 1 is operated in the positive-pressure state to a degree in which the load is not generated. In a case where the space in cylinder 1 e of compressor 1 becomes the excessively positive pressure, nitrogen discharge control valve 80 b is opened to discharge the nitrogen in buffer tank 4. This enables compressor 1 to be stably operated.

According to the cooling system of the present embodiment described above, the nitrogen serving as the refrigerant is used in the circulating manner, and the need for supplying the new refrigerant is eliminated. Therefore, because the running cost is required only for the cost of electric power consumption of compressor 1, the cost reduction can largely be achieved as compared with the cooling system discharging sequentially the nitrogen.

Although the invention has been described in detail only by way of example, the invention should not be limited thereto, but it is to be apparently understood that the scope of the invention is limited only by the appended claims. 

1. A cooling system comprising: a compressor to compress a gas refrigerant except air to a degree in which the gas refrigerant is not liquefied and to deliver the gas refrigerant; a heat source to be cooled by said gas refrigerant when the gas refrigerant delivered from said compressor passes therethrough; a heat exchanger in which said gas refrigerant dissipates heat to an outside after absorbing the heat from said heat source; a buffer tank in which said gas refrigerant is temporarily accumulated after dissipating the heat to the outside in said heat exchanger; and piping to couple said compressor, said heat source, said heat exchanger, and said buffer tank in that order to constitute a closed circuit, said gas refrigerant being circulated through the closed circuit.
 2. The cooling system according to claim 1, further comprising another buffer tank between said compressor and said heat source to temporarily accumulate said gas refrigerant therein.
 3. The cooling system according to claim 1, wherein a volume of said buffer tank is not lower than an amount of said gas refrigerant discharged by said compressor within a time necessary to circulate said gas refrigerant once in said closed circuit.
 4. The cooling system according to claim 1, further comprising: replenishing piping connected to said buffer tank to replenish said gas refrigerant from the outside; and discharging piping connected to said buffer tank to discharge said gas refrigerant to the outside.
 5. The cooling system according to claim 1, wherein said compressor has an ability to discharge an amount of said gas refrigerant larger than a circulating amount of said gas refrigerant necessary to cool said heat source to a target temperature.
 6. The cooling system according to claim 1, wherein said gas refrigerant contains nitrogen, oxygen, carbon dioxide, or inert gas.
 7. The cooling system according to claim 1, wherein said piping acts as a cooling tube in said heat source, and a surface area of said cooling tube is in a range of 20 cm² to 750 cm² per 1 m³ of the heat source.
 8. The cooling system according to claim 1, wherein pressure loss of gas in said heat exchanger is not more than one-tenth of pressure loss of gas in said entire closed circuit.
 9. The cooling system according to claim 1, further comprising a refrigerant supply path aside from said closed circuit, said refrigerant supply path supplying said gas refrigerant having an amount discharged by said compressor to said compressor until said gas is circulated once in said closed circuit since said compressor is started up.
 10. The cooling system according to claim 1, further comprising: an exhaust valve to automatically exhaust said gas refrigerant in said buffer tank when a pressure of said gas refrigerant in said buffer tank is substantially equal to an upper limit of a suction pressure of said compressor; and a suction valve to automatically suck said gas refrigerant into said buffer tank when the pressure of said gas refrigerant in said buffer tank is substantially equal to a lower limit of the suction pressure of said compressor.
 11. A plasma processing system comprising: a compressor to compress a gas refrigerant except air to a degree in which the gas refrigerant is not liquefied and to deliver the gas refrigerant; a plasma processing apparatus to generate heat when a predetermined process is performed using a plasma processing gas, the apparatus being cooled by said gas refrigerant when the gas refrigerant delivered from said compressor passes therethrough; a heat exchanger in which said gas refrigerant dissipates heat to an outside after absorbing the heat from said heat source; a buffer tank in which said gas refrigerant is temporarily accumulated after dissipating the heat to the outside in said heat exchanger; and piping to couple said compressor, said heat source, said heat exchanger, and said buffer tank in that order to constitute a closed circuit, said gas refrigerant being circulated through the closed circuit, wherein said gas refrigerant includes one or more gases which does not react with said plasma processing gas.
 12. A method for operating the cooling system according to claim 1, the method comprising the steps of: sucking said gas refrigerant into said buffer tank by a decrease in pressure of said gas refrigerant in said buffer tank when said compressor is started up; and maintaining a pressure of said gas in said buffer tank at a value of a degree in which said compressor is not broken, after a time longer than a time necessary to circulate said gas refrigerant once in said closed circuit elapses. 